docs: def _fit(y, classes):
      """Calculate the total sum of squares for a vector y classified into
      classes
  
      Parameters
      ----------
      y : array
          (n,1), variable to be classified
  
      classes : array
                (k,1), integer values denoting class membership
  
      """
      tss = 0
      for class_def in classes:
          yc = y[class_def]
          css = yc - yc.mean()
          css *= css
          tss += sum(css)
      return tss